I got a reply from ACRI

Hi Victoria,
Thankyou for your feedback. This section definitely requires a re-edit so it’s up to date others and does not promote further confusion. I do not understand how this has been missed but we will rectify it today.
So I think this answers - the weight limit on an integral harness part - if you have a seat with height markers on it - then the integral harness is not weight restricted (so all the new seats - new standard from 2010). If no height markers, then is probably best to contact the manufacturer (as ZF did) to check.

(There must be some weight restriction on the integral harness though determined by what they test to which is probably about 32kg - so I am still of the opinion that the guidelines are not clear enough).